Commutator bar and method of making same



Aug. 22, 1950 P. R. BLAIR COMMUTATOR BAR AND METHOD OF MAKING SAME 2 Sheets-Sheet 1 Filed May 2, 1945 INVENTOR. Bu/L R; BLA/R Aug. 22, 1950 P. R. BLAIR 2,519,626

COMMUTATOR BAR AND METHOD OF MAKING SAME Filed May 2, 1945 2 Sheets$heet 2 fia/ bk/7 INVENTOR.

BY 540/. 5. 152m //4 Patented Aug. 22, 1950 'COMMUTATOR BAR AND METHOD OF MAKING SAME Paul R. Blair, Cleveland Heights, Ohio Application May 2, 1945, Serial No. 591,548

8 Claims.

My invention pertains to a commutator bar for an electric motor and/r electric generator.

An object of my invention is to provide a new and improved commutator bar.

Another object of my invention is to provide a light and inexpensive commutator bar.

A further object of my invention is to provide a method of making a light, inexpensive commutator bar.

It is also an object of my invention to provide a stamped commutator bar of a size which hitherto has been impractical to form by stamping.

Still another object of the invention is to reduce the number of expensive time-consuming operations necessary to form a commutator bar.

And another object of the invention is to reduce scrap material incident to the manufacture of commutator bars.

Other objects and a fuller understanding of my invention will be had by referring to the following description and drawings, wherein:

Figure 1 is a plan view of a blank from which my commutator bar is made.

Figure 2 is an isometric view of the new commutator bar.

Figure 3 is a sectional view taken along line 3-3 of Figure 2.

Figure 4 is a sectional view taken along line 4-4 of Figure 2.

Figure 5 is a sectional view taken through a simplified form of commutator and showing commutator bars in position.

Figure 6 is a sectional view of a partially formed commutator bar illustrating one step in the manufacture of another form of my invention.

Figure 7 illustrates the device of Figure 6 fully formed and nested with another similar commutator bar, and

Figures 8 to 17 illustrate the steps in the process of making the commutator bar shown in Figure 7.

By my invention I provide a commutator bar which is cheaper to manufacture and which is lighter in weight than previously known commutator bars, yet which is strong and is capable of carrying large amounts of electric current.

The commutator bar of my invention is formed either by stamping and bending sheet metal or by rolling and coining thin sheet or bar stock into the desired shape. In either case there results a commutator bar which is not solid and which, therefore, is much lighter than a solid bar.

The first step in the process of making the sheet metal commutator bar is to provide a, sheet 2 of the required metallic material such as copper, steel or the like, and, as shown by Figure 1, to blank out the form ID from which the commutator bar is made. The desired thickness of the sheet of metal will vary depending upon the size of the commutator which is to be made, but in order to achieve the objects of my invention the sheet material should be considerably thinner than the maximum thickness of the commutator bar to be made. By the thickness of the commutator bar, I mean the distance between the nesting faces of the bar. For example, I have found that for a commutator bar which is of an inch thick at its wearing surface sheet steel of an inch thick bent or formed in accordance with my invention is satisfactory, although it is possible to use other thicknesses and to use other materials. If a relatively soft copper is used the thickness of the sheet should be somewhat greater.

The blanked form 10 has two main portions, a body portion II and a dovetail portion [2 which preferably are integral with each other. Ac-

cordingly, a simple stamping operation is sufficient to produce the blank from which the commutator bar is made, and due to the fact that the metal is thin compared to the thickness of the commutator bar to be made, it is possible to stamp out blanks for making commutator bars of large size. This is a distinct advance over the known art as previously it has not been possible to stamp out commutator bars of the larger sizes from metal as thick as the finished commutator bar.

After the stamping operation the blank IQ is folded along line A-A through an angle of about 180 degrees so that the body portion is folded back upon itself forming a hollow channel, the hollow being identified in Figure 2 by reference character l5. The top surface iii of this channel is the wearing surface, and its width is approximately the width of the cummutator bar. Another folding operation bends the blank iii in the opposite direction along line 3-3 through an angle somewhat less than 180 degrees, for example, about 150 degrees, and it is folded through an angle of about degrees along line C-C in the same direction as the fold A-A to bring the lower edge I! of the dovetail portion 1 l substantially directly under the center line of the wearing surface [6, as is shown in Figure 4.

Preferably, the general shape of the commutator bar after these three folding operations is like a narrow V, as will be seen in Figure 4. This facilitates forming a commutator from a plurality of the commutator bars as the bars have the general shape of a small sector of a circle.

After the A, B, and C folding operations, the device is folded along line DD (Figure 1) to form a tang 20 extending substantially perpendicular to the wearing surface l6. Because of the substantially 180 degree fold along line A-A, the tang 28 is formed of a double thickness of metal, and these two thicknesses are squeezed together, as shown in Figure 2. This double thickness is advantageous as the tang 2i) has the heaviest current concentration of any portion of the commutator bar.

Figure 5 illustrates by a schematic cross-sectional view the manner in which a number of the formed commutator bars 2! are connected together to make a commutator. The commutator bars 2| carry insulation 22, such as mica rings or the like, on their underneath surfaces as is known to the art, and rings 23 having portions 2 which engage the insulation 22 at the dovetail portion I! are bolted together by bolts 25 to hold the assembly together.

Figures 6 to 1'? illustrate steps in the manufacture of a commutator bar, which, while differing from the bar shown in Figure 2, is within the scope of my invention. The device shown in Figure 6 may be rolled from a long strip of metal having a width about equal to the height of the device shown in Figure 6. This step is shown in Figures 8 to 11, wherein Figures 8 and 9 are side and end views, respectively, of the strip of metal from which the commutator bar is formed, and

Figures 10 and 11 are side and end views after the strip shown in Figures 8 and 9 has been rolled. After the preliminary rolling or forming operation, the device is blanked, as shown in Figures 12 and 13 and one end is then bent through an angle of about 90 degrees to form the tang 2?! as is shown in Figures 14 and 15. The bar is then coined into the final shape which is shown in Figures 16 and 17, resulting in the commutator bar 30 shown in Figure '7. A plurality of these commutator bars 383 are put together with mica insulators 3| between them. Due to the more nearly square corners of the commutator bar 38 better bearing surfaces for the insulators 3! are provided.

It will be appreciated that the aforedescribed commutator bar which may be formed of sheet metal having a thickness of only about one-sixth the thickness of the bar across the wearing surface I6 will effect a tremendous saving in material over the usual solid commuator bar, and due to the folding operation its strength and current carrying capacity will be sufficient for all applications. Further, due to the simplicity of the device, many operations in the manufacture of commutator bars has been eliminated, such, for example, as the tapering of the solid commutator bars in order to facilitate stacking them into a circular commutator. And still further, by making the commutator bar of sheet metal which is thin compared to the thickness of the finished commutator bar, the invention permits using stampings in the large sizes where previously the bars were machined.

It will also be appreciated that the process of manufacturing my new commutator bar results 70 in much less scrap metal than previous methods which not only had scrap due to the stamping operation but had scrap due to machining operations.

A further important feature of my commut tor 7 4 bar is that due to the configuration of its side faces a number of them can be held together by plastic material either with or without other holding means to form a commutator. Previous commutator bars had smooth side faces, and the side faces of the adjacent bars in a commutator were substantially parallel. Plastic material be tween them would not serve to hold them together and, further, there waslittle or no space not occupied by a separating insulator into which plastic material could be forced. The plastic which is forced between my new bars to form a commutator preferably should have the same coefficient of thermal expansion as the metal used for the bars, and after the plastic sets the commutator is, in effect, an integral unit which is firmly held together with the plastic serving to damp the vibrations in the commutator.

Although I have described my invention with a certain degree of particularity it is to be understood that changes may be made in the steps of the process and in the arrangement of the device without departing from the spirit and scope of m invention.

I claim as my invention:

1. A commutator bar formed of a sheet of metal whose thickness is less than the thickness of the body portion of said bar,'said body portion having at one edge thereof a wearing surface and at its opposite edge a dovetail portion, said sheet eX- tending in a direction substantially normal to the radial axis of said bar for a given distance to form said wearing surface and bending in one direction through an angle greater than degrees back upon itself and extending fora distance substantially equal to I said given distance to form a light Weight rigid body portion, and said sheet being bent in the opposite direction substantially at the point where the body portion becomes the dovetail portion.

2. A commutator bar as set forth in claim 1, further characterized in this: that the sheet metal in said dovetail portion is also bent,

3. A commutator bar as set forth in claim 1, further characterized in this: that said sheet metal in said dovetail portion is also bent, and the thickness of the dovetail portion is less than the thickness of the body portion, whereby a plurality of said commutator bars laid side-byside with the wearing surface outward define substantially a cylinder.

4. A commutator bar formed of a sheet of metal whose thickness is less than the thicknessof the body portion of said bar, one edge of said sheet extending substantially normal to the radial axis of said bar for a given distance to form a commutator wearing surface and bending back more than 90 degrees upon itself to form a surface underneath and spaced substantially throughout its entire length from the said wearingsurface, the current carrying tang of said bar comprising" one end of said wearing surface and the corresponding end of said underneath surface in face+toface engagement with each other whereby said tang is twice the thickness of said sheet metal to facilitate carrying the required amount of current.

5. A commutator bar formed of sheet metal Whose thickness is less than the thickness, of the body portion of said bar, said body portion com prising a wearing surface portion and a central portion, and a dovetail portion connected to said central portion, said central portion being connected tosaid wearing surface portion atonly one d i th Wearing surface portion, and said central portion and said dovetail portion including at least one corrugation to stiffen said bar.

6. A commutator bar as set forth in claim 5 further characterized by a current carrying tang at an angle to the wearing surface portion, said tang comprising one end of said Wearing surface portion, and the corresponding end of the corrugation immediately adjacent said wearing surface portion in face-to-face engagement with each other whereby the thickness of said tang is twice the thickness of said sheet metal to facilitate carrying the required amount of current.

7. A commutator bar formed of a sheet of metal whose thickness is less than the thickness of the body portion of said bar, said body portion comprising a central portion and an integrally connected wearing surface portion at one edge thereof, a dovetail portion connected to the opposite edge of said central portion, said sheet extending in a direction substantially normal to the radial axis of said bar for a given distance to form said wearing surface portion and bending in one direction through an angle greater than 90 degrees back upon itself and extending for a distance less than said given distance to form a corrugation in said body portion, and said sheet being bent in the opposite direction substantially at the point where the body portion is connected to the dovetail portion.

8. A commutator bar formed of sheet metal whose thickness is less than the thickness of the 30 body portion of said bar, said body portion comprising a central portion and an integrally connected wearing surface portion at one edge thereof, a dovetail portion connected to the opposite edge of said central portion, said central portion being connected to said wearing surface portion at only one side of the wearing surface portion, and said body portion and said dovetail portion including a series of corrugations to stiffen said bar, the edge of said dovetail portion away from the said body portion lying substantially on the radial axis of said bar.

PAUL R. BLAIR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,332,324 Crowe Mar. 2, 1920 1,360,165 Zenk Nov. 23, 1920 1,401,016 Volte Dec. 20, 1921 1,472,023 Koos Oct. 23, 1923 1,845,115 Apple Feb. 16, 1932 1,898,696 Sorensen Feb. 21, 1933 1,898,929 Apple Feb. 21, 1933 1,905,413 Kramer Apr. 25, 1933 2,244,847 Oeckl June 10, 1941 FOREIGN PATENTS Number Country Date 511,315 Germany of 1930 

